aboutsummaryrefslogtreecommitdiff
path: root/samples/kobject/kset-example.c
blob: 3b126d1f8599198e6930ff7bd3c5690fb52ec138 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
/*
 * Sample kset and ktype implementation
 *
 * Copyright (C) 2004-2007 Greg Kroah-Hartman <greg@kroah.com>
 * Copyright (C) 2007 Novell Inc.
 *
 * Released under the GPL version 2 only.
 *
 */
#include <linux/kobject.h>
#include <linux/string.h>
#include <linux/sysfs.h>
#include <linux/module.h>
#include <linux/init.h>

/*
 * This module shows how to create a kset in sysfs called
 * /sys/kernel/kset-example
 * Then tree kobjects are created and assigned to this kset, "foo", "baz",
 * and "bar".  In those kobjects, attributes of the same name are also
 * created and if an integer is written to these files, it can be later
 * read out of it.
 */


/*
 * This is our "object" that we will create a few of and register them with
 * sysfs.
 */
struct foo_obj {
	struct kobject kobj;
	int foo;
	int baz;
	int bar;
};
#define to_foo_obj(x) container_of(x, struct foo_obj, kobj)

/* a custom attribute that works just for a struct foo_obj. */
struct foo_attribute {
	struct attribute attr;
	ssize_t (*show)(struct foo_obj *foo, struct foo_attribute *attr, char *buf);
	ssize_t (*store)(struct foo_obj *foo, struct foo_attribute *attr, const char *buf, size_t count);
};
#define to_foo_attr(x) container_of(x, struct foo_attribute, attr)

/*
 * The default show function that must be passed to sysfs.  This will be
 * called by sysfs for whenever a show function is called by the user on a
 * sysfs file associated with the kobjects we have registered.  We need to
 * transpose back from a "default" kobject to our custom struct foo_obj and
 * then call the show function for that specific object.
 */
static ssize_t foo_attr_show(struct kobject *kobj,
			     struct attribute *attr,
			     char *buf)
{
	struct foo_attribute *attribute;
	struct foo_obj *foo;

	attribute = to_foo_attr(attr);
	foo = to_foo_obj(kobj);

	if (!attribute->show)
		return -EIO;

	return attribute->show(foo, attribute, buf);
}

/*
 * Just like the default show function above, but this one is for when the
 * sysfs "store" is requested (when a value is written to a file.)
 */
static ssize_t foo_attr_store(struct kobject *kobj,
			      struct attribute *attr,
			      const char *buf, size_t len)
{
	struct foo_attribute *attribute;
	struct foo_obj *foo;

	attribute = to_foo_attr(attr);
	foo = to_foo_obj(kobj);

	if (!attribute->store)
		return -EIO;

	return attribute->store(foo, attribute, buf, len);
}

/* Our custom sysfs_ops that we will associate with our ktype later on */
static const struct sysfs_ops foo_sysfs_ops = {
	.show = foo_attr_show,
	.store = foo_attr_store,
};

/*
 * The release function for our object.  This is REQUIRED by the kernel to
 * have.  We free the memory held in our object here.
 *
 * NEVER try to get away with just a "blank" release function to try to be
 * smarter than the kernel.  Turns out, no one ever is...
 */
static void foo_release(struct kobject *kobj)
{
	struct foo_obj *foo;

	foo = to_foo_obj(kobj);
	kfree(foo);
}

/*
 * The "foo" file where the .foo variable is read from and written to.
 */
static ssize_t foo_show(struct foo_obj *foo_obj, struct foo_attribute *attr,
			char *buf)
{
	return sprintf(buf, "%d\n", foo_obj->foo);
}

static ssize_t foo_store(struct foo_obj *foo_obj, struct foo_attribute *attr,
			 const char *buf, size_t count)
{
	sscanf(buf, "%du", &foo_obj->foo);
	return count;
}

static struct foo_attribute foo_attribute =
	__ATTR(foo, 0666, foo_show, foo_store);

/*
 * More complex function where we determine which variable is being accessed by
 * looking at the attribute for the "baz" and "bar" files.
 */
static ssize_t b_show(struct foo_obj *foo_obj, struct foo_attribute *attr,
		      char *buf)
{
	int var;

	if (strcmp(attr->attr.name, "baz") == 0)
		var = foo_obj->baz;
	else
		var = foo_obj->bar;
	return sprintf(buf, "%d\n", var);
}

static ssize_t b_store(struct foo_obj *foo_obj, struct foo_attribute *attr,
		       const char *buf, size_t count)
{
	int var;

	sscanf(buf, "%du", &var);
	if (strcmp(attr->attr.name, "baz") == 0)
		foo_obj->baz = var;
	else
		foo_obj->bar = var;
	return count;
}

static struct foo_attribute baz_attribute =
	__ATTR(baz, 0666, b_show, b_store);
static struct foo_attribute bar_attribute =
	__ATTR(bar, 0666, b_show, b_store);

/*
 * Create a group of attributes so that we can create and destroy them all
 * at once.
 */
static struct attribute *foo_default_attrs[] = {
	&foo_attribute.attr,
	&baz_attribute.attr,
	&bar_attribute.attr,
	NULL,	/* need to NULL terminate the list of attributes */
};

/*
 * Our own ktype for our kobjects.  Here we specify our sysfs ops, the
 * release function, and the set of default attributes we want created
 * whenever a kobject of this type is registered with the kernel.
 */
static struct kobj_type foo_ktype = {
	.sysfs_ops = &foo_sysfs_ops,
	.release = foo_release,
	.default_attrs = foo_default_attrs,
};

static struct kset *example_kset;
static struct foo_obj *foo_obj;
static struct foo_obj *bar_obj;
static struct foo_obj *baz_obj;

static struct foo_obj *create_foo_obj(const char *name)
{
	struct foo_obj *foo;
	int retval;

	/* allocate the memory for the whole object */
	foo = kzalloc(sizeof(*foo), GFP_KERNEL);
	if (!foo)
		return NULL;

	/*
	 * As we have a kset for this kobject, we need to set it before calling
	 * the kobject core.
	 */
	foo->kobj.kset = example_kset;

	/*
	 * Initialize and add the kobject to the kernel.  All the default files
	 * will be created here.  As we have already specified a kset for this
	 * kobject, we don't have to set a parent for the kobject, the kobject
	 * will be placed beneath that kset automatically.
	 */
	retval = kobject_init_and_add(&foo->kobj, &foo_ktype, NULL, "%s", name);
	if (retval) {
		kobject_put(&foo->kobj);
		return NULL;
	}

	/*
	 * We are always responsible for sending the uevent that the kobject
	 * was added to the system.
	 */
	kobject_uevent(&foo->kobj, KOBJ_ADD);

	return foo;
}

static void destroy_foo_obj(struct foo_obj *foo)
{
	kobject_put(&foo->kobj);
}

static int __init example_init(void)
{
	/*
	 * Create a kset with the name of "kset_example",
	 * located under /sys/kernel/
	 */
	example_kset = kset_create_and_add("kset_example", NULL, kernel_kobj);
	if (!example_kset)
		return -ENOMEM;

	/*
	 * Create three objects and register them with our kset
	 */
	foo_obj = create_foo_obj("foo");
	if (!foo_obj)
		goto foo_error;

	bar_obj = create_foo_obj("bar");
	if (!bar_obj)
		goto bar_error;

	baz_obj = create_foo_obj("baz");
	if (!baz_obj)
		goto baz_error;

	return 0;

baz_error:
	destroy_foo_obj(bar_obj);
bar_error:
	destroy_foo_obj(foo_obj);
foo_error:
	return -EINVAL;
}

static void __exit example_exit(void)
{
	destroy_foo_obj(baz_obj);
	destroy_foo_obj(bar_obj);
	destroy_foo_obj(foo_obj);
	kset_unregister(example_kset);
}

module_init(example_init);
module_exit(example_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Greg Kroah-Hartman <greg@kroah.com>");